The development of leading industries is accompanied by a continuous increase in the range and scope of manufactured materials featuring high service properties (for example, heat-resisting, extrahard materials, materials having desired electronic or electrotechnical characteristics, etc.) but poor machinability. At the same time the requirements to the quality of machining of such materials are ever growing, the main requirements being the following: absence of defects, for example chipping, microcracks, burns in the surface layer of articles, and a low suerface roughness.
Besides, there exist such general requirements as a high productive capacity and a reasonable wear of grinding tools from the view point of technology and economy. To satisfy all these requirements using the traditional methods of abrasive grinding is not possible in most of the cases. Thus, for grinding such difficult-to-work materials use is frequently made of a method of diamond-electrochemical grinding which combines processes of microcutting and electrochemical removal of workpiece metal. However, this method has a number of disadvantages limiting and hindering its use.
The main of such disadvantages are use of electrolyte solutions as working media owing to which the most vital units of machines have to be manufactured from corrosion-resisting materials; large dimensions, high cost and complicated maintenance of the diamond-electrochemical grinding machines; a high power consumption of the method, large operating currents (up to several thousands of amperes).
There is known in the art a method of abrasive electroerosion grinding of difficult-to-work materials (SU, A, No. 841,889) using a metallic-bond wheel and a coolant, whereby a pulse voltage is applied to the wheel in a zone of grinding of a workpiece and an electrode is arranged out of that zone to produce an additional electric action upon the wheel. The use of noncorrosive coolants as working media for carrying out this method makes it possible to employ the existing grinding materials, and, in the newly developed machines, to use ordinary structural materials. Moreover, the method according to SU, A, No. 841,889 compared with the diamond-electrochemical method has the following advantages: a ten-fold factor of time reduction in working current (not above 50 A): a 15-20% decrease in power consumption; dimensions of the auxiliary equipment (tanks, cleaning systems, power supply sources) reduced by a factor of 2-4.
However, when carrying out this prior art method of abrasive-electroerosion grinding the wear of the abrasive tool remains considerable (from 5 to 30 mg/g) which results in great consumption of the wheels and requires frequent replacement thereof; the machining is accompanied with comparatively strong sparking, luminous radiation and noise; in a number of cases (for example in highly productive rough grinding) the cutting properties of the abrasive tool cannot be stabilized with the aid of electric action.
The main cause of such disadvantages is conductance (though inconsiderable) of the working media used, which results in a reduction of the dielectric strength of the interelectrode space. This drawback brings about a reduced voltage at the power source output, losses of energy into the surrounding conducting medium, unsatisfactory localization of discharges on the surface of the electrodes. To make up for these losses, it is necessary to increase a pulse voltage amplitude and power of the power source which results in an increase in noise, luminous radiation and in wear of the wheels. Using organic liquids (kerosene, oil, etc.) as a working medium which is in common practice with the electroerosion machines is inadmissible in the case of the grinding machines because of the risk of ignition of the liquid atomized by the wheel rotating at a speed of 15-30 m/s.